The present invention relates to a filter element suitable for use in various type of filters such as a vehicle fuel filter and oil filter, for example, and a manufacture method thereof.
For improvement of filter performance, instead of conventional filter elements formed by bending a sheet-like filtering material into the shape of flower leaves or a chrysanthemum in cross-section, there are proposed filter elements of honeycomb structure having an larger effective filtration area per unit volume.
For example, Japanese Patent Publication No. 61-50612 or U.S. Pat. No. 2,599,604 discloses a filter element which is fabricated by fusing a flat filtering material and a corrugated filtering material to each other, and then rolling the assembly into a spiral shape to provide a cylindrical laminate with a number of small through holes.
In the filter element thus constructed, as shown in FIG. 36, one end face of the cylindrical laminate is sealed off at inlets of flow passages 91 defined by valley-like portions 71 of a corrugated filtering material 7 and a flat filtering material 8, whereas the other end face thereof is sealed off at outlets of flow passages 92 defined by mountain-like portions 72 of the corrugated filtering material 7 and the flat filtering material 8, while leaving the outlets of the flow passages 91 open. A fluid to be filtered is introduced to the inlets of the passages 92, and the cleaned filtrate is then taken out from the outlets of the passages 91 after passing through the filtering materials 7, 8 for filtration.
However, the above-mentioned structure of the prior art has a disadvantage. The differential pressure between the flow passages 92 on the inlet side and the flow passages 91 on the outlet side is so increased due to such factors as the pressure of the fluid to be filtered or clogging of the filtering materials that the flat material 8 is deformed (as indicated by dotted lines in FIG. 37). This narrows and even blocks the flow passages 91 on the outlet side, resulting in degradation of filter performance.
Another problem is in that when rolling the filtering materials together into a spiral shape, the flow passages may be collapsed because of a difference in circumferential length between the inner-side flat filtering material 8 and the outer-side corrugated filtering material 7.